This invention was made with United States Government support under a contract with the United States Navy. The government has certain rights in this invention.
The present invention relates generally to high current electrical connectors, and more specifically to such connectors suitable for use in providing an electrical connection to the main field coil on a generator or motor rotor.
Large electrical motors and generators are used in industrial plants and processes, for generation of electric power, and also for marine or shipboard use. In marine applications they are frequently utilized in the generation of electrical power; and in ships' propulsion systems, that is, in providing the power for driving the ships' propellers. In these and other applications, such large motors and generators are frequently subjected to repeated starts and stops. Failures of such large generators or motors are considered serious matters and reliability of operation is a prime requirement for such machines. Failures can seriously affect operations of industrial plants and power systems, and in the case of marine applications, the ability of the ship to supply necessary power and even the ability to maneuver and maintain headway. As an example of the extreme reliability required for marine applications, customer specifications may require that marine installations meet a cyclic duty requirement of well in excess of fifty thousand starts and stops. Moreover, in order to provide assurance of meeting such stringent requirements, generators and motors have to be designed for reliable start/stop cyclic duty requirements which are well in excess of the required number.
The problem of repeated start/stop cycling of large generators and motors having substantial size and weight results from significant inertial and thermal forces and strains on the various components of such generators and motors. Components at a distance from the axis of the generator or motor are, for example, subjected to significant centrifugal forces in which the restrained components react against the restraint with a force directed away from the center of curvature of its path. This centrifugal force is directly related to the product of the mass of the body and its centripetal acceleration. Such forces are of particular concern in large generators and motors where components are located significant distances from the axis of rotation. Such components include field coils disposed about the rotors and restrained from moving outward away from the generator or motor axis and core by restraining means such as adhesives, coil wedges, and retaining rings and other restraining mechanisms.
Electrical connectors which connect the field coils to terminals for connection, for example, to the field exciter are subjected to various forces, including centrifugal force and forces tending to move the field coils relative to the rotor each time the generator or motor is started or stopped. Concern has arisen tat such connectors are potential weak links in such generators and motors.
One connector designed to withstand repeated start/stop cycles utilizes a leaved structure composed of many thin copper leaves joined together to provide a single piece connector. To provide for limited movement and resist repeated stresses due to the start/stop cycles, its general configuration includes a U-shaped or hairpin bend. The upper jaw of the hairpin is parallel to and connected to, the field coil. The lower jaw includes at its end remote from the apex of the jaws, a perpendicular section, or downwardly extending portion, connected to a terminal which extends through the rotor to the field exciter. This terminal enables connection to an exciter which provides direct current (DC) to power the generator field coil. In such an arrangement, the multiple leaves extend from the field coil parallel to the axis of rotation of the generator and then extend through the hairpin or U-shaped curve to then be bent at substantially a right angle, for connection to the radially extending terminal. The thickness of each jaw about the apex is much less than the width of the jaws to facilitate flexing of the jaws to absorb flexing forces which tend to close the jaws. With such an arrangement, the principal inertial forces generated by start/stop cycles between the coils and the terminal are applied across the jaws of the hairpin to tend to flex the jaws in order to absorb such movements and forces.
Such a connector arrangement has proven effective and reliable in operation for many applications. However, the need for increased reliability, and in particular the ability to withstand increased cycles of start/stop operation, and the need to withstand fatigue failures over such increased cycles, has led to the need for a more reliable connector which will withstand increased start/stop cycles.